This invention generally relates to the application of adhesive to the ends of rod-shaped members and, more particularly, to the ends of rods or sticks used for manufacturing of cotton swabs.
Various manufacturing processes involve affixing elements to one or both ends of a rod-shaped member. One specific application for such a process is the manufacture of cotton swabs. Such products may be manufactured with cotton fibers or other types of fibers secured to one or both ends of a paper, plastic or wooden stick with adhesive. During manufacture, it is important to properly apply the adhesive to one or both ends of the stick before application of the cotton fibers. Too little adhesive will result in unsatisfactory adherence of the fibers to the stick, while excessive adhesive application will result in undesirable manufacturing downtime due to the clean up of adhesive dripping or otherwise being flung from the stick during the manufacturing process. While meeting the precise quantity requirements of adhesive application, the manufacturing process must also consistently apply the adhesive around the end or ends of each stick and must do so in a high speed manufacturing environment to hold product manufacturing costs as low as possible.
One current process for manufacturing cotton swabs involves rapidly conveying the sticks past a rotating wheel which has a lower portion thereof in contact with a container of adhesive. The adhesive therefore continually coats the circumference of the wheel. As the ends of each stick contact the upper portion of the spinning wheel, the ends are simultaneously rotated and coated with the adhesive. While this method allows for a rapid production speed, the above noted problems exist with this type of process. Specifically, the wheel can accumulate too much adhesive on its circumference and, therefore, apply too much adhesive to the ends of the stick. Some of this adhesive will fall or be flung off the ends of the stick necessitating manufacturing downtime in order to clean up the excess adhesive. Also, because the adhesive is exposed to the environment prior to its application on the stick, the adhesive can accumulate various airborne contaminates. This can reduce the effectiveness of the adhesive and lead to unsatisfactory adherence of the fibers to the stick. The use of a wheel to apply adhesive to the sticks may also lead to inconsistent adhesive deposition as a result of inconsistent amounts of adhesive on the circumference of the wheel. For example, as the level of adhesive in the adhesive supply becomes reduced, there may be less adhesive applied to the circumference of the wheel and, conversely, when the supply is increased, increased adhesive contact is made with the wheel resulting in increased amounts of adhesive on the wheel. These characteristics of this existing process correspondingly result in decreased or increased amounts of adhesive being applied to the ends of the sticks.
Another previously proposed manufacturing method for cotton swabs generally involves the use of an on/off adhesive dispensing valve having slot nozzles positioned in the respective paths of the ends of the sticks. The sticks move over the slot nozzles which are activated and the sticks simultaneously rotate such that the ends of the sticks receive the discharged adhesive. The challenge associated with this proposed method is that the rod or stick must be rotated quickly enough as it passes the slot nozzles to ensure coating of the entire circumference of each end. In order for this to occur, line speeds may have to be reduced to an undesirably low level or spinning rates of the sticks may have to be increased to an impractically high level. Even if the speeds are adjusted to ensure a full rotation directly over the slot nozzle, the slot nozzle may still not apply adhesive in an evenly distributed amount to the entire outer surface of each stick end.
For these and other reasons, it would be desirable to provide a system and method for applying adhesive to one or both ends of a rod-shaped member in a uniform, consistent manner, and in precise amounts, while maintaining the high manufacturing speeds necessary to hold down product manufacturing costs.
In one general aspect, the present invention provides a system for applying adhesive to at least a first end of a rod-shaped member. The system generally includes a carrier, an adhesive applicator, and a rotator device. The carrier is configured to convey the rod-shaped member in a machine direction while allowing rotation of the rod-shaped member about its longitudinal axis. The adhesive applicator preferably includes an application surface positioned to engage the first end of the rod-shaped member. At least one adhesive discharge passage is provided to apply adhesive to the first end. For example, the discharge passage may extend through the application surface to apply adhesive to the first end. The rotator device is positioned preferably on a generally opposite side of the rod-shaped member relative to the application surface and rotates the rod-shaped member about its longitudinal axis as the rod-shaped member is conveyed along the application surface.
The application surface is preferably elongate in the machine direction and angled toward the carrier. The application surface has at least a portion that engages the first end for at least substantially an entire revolution thereof in order to evenly distribute the adhesive around the first end. The rotator device is preferably a stationary belt or other friction inducing surface configured to engage an area of the rod-shaped member other than the first end. For example, in the preferred embodiment, the belt contacts the central area of the rod-shaped member, e.g., the stick of a cotton swab, but does not contact the ends of the rod-shaped member which receive the adhesive and later receive the cotton fibers. Angling the application surface toward the carrier allows the belt to apply pressure to the center of the rod-shaped member while ensuring that the ends thereof maintain contact with the application surface. This helps ensure uniform adhesive application. As the rod-shaped member approaches the application surface, it is moved in a direction toward the rotator device, such as the belt. This is accomplished in the preferred embodiment by using an inclined surface immediately upstream of the adhesive application surface. Of course, other engagement structure may be used instead and may be partly or wholly provided on the carrier or another portion of the system. Preferably, the carrier includes a slot allowing the rod-shaped member to move upward along the inclined surface until it contacts the belt. Other rotator devices may be used as well.
The application surface preferably has multiple adhesive discharge passages spaced transversely relative to the machine direction and associated grooves extending in the machine direction aligned with the discharge passages and extending downstream therefrom. Thus, the adhesive is initially discharged and applied to the end of the rod-shaped member and the rod-shaped member is rotated by the belt along a downstream portion of the application surface. The grooves help ensure that a uniform thickness of adhesive is distributed, preferably in bands about the entire outer surface of the rod end. The grooves are preferably directly aligned with one or more corresponding adhesive discharge passages.
The carrier can be constructed as a link in a chain-like structure which moves along the manufacturing line at high speed, such as on the order of 2500 cotton swabs per minute. The carrier has slots on opposite sides thereof which receive respective end portions of the rod-shaped member and identical adhesive applicators are positioned on opposite sides of the carrier. One or more on/off dispensing valves are used to supply adhesive to the adhesive discharge passages. A sensor is used to detect the presence of each oncoming rod-shaped member and communicates with a control to ensure proper timing of the activation of the valve(s) such that the adhesive is dispensed effectively onto the ends of the rod-shaped member.
The invention further contemplates methods of applying adhesive to at least a first end of a rod shaped member. The method generally involves conveying the rod-shaped member in a machine direction with the longitudinal axis thereof extending transverse to the machine direction. The rod-shaped member is rotated about its longitudinal axis and adhesive is applied to the first end thereof from an adhesive discharge passage in an adhesive application surface. Contact is maintained between the rotating first end of the rod-shaped member and the adhesive application surface downstream of the discharge passage to distribute the discharged adhesive around the first end. The methods of this invention also generally contemplate the processes of using other novel aspects of this invention.
These and other features and objectives of the present invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings.